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Change FNV1A Meiyan hash by FNV1A Jesteress

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Patrick Pelissier committed 2017-04-18 23:21:53 +02:00
1 parent 02be3b6d69
commit b60cc58980
1 file changed
+22 -18
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m-core.h
+22 -18
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@@ -650,37 +650,41 @@ static inline uint32_t m_core_rotl32a (uint32_t x, uint32_t n)
return (x<<n) | (x>>(32-n)); return (x<<n) | (x>>(32-n));
} }
/* Implement Meiyan Hash /* Implement FNV1A Jesteress Hash (very similar to FNV1A Meiyan Hash)
See https://www.strchr.com/hash_functions & http://www.sanmayce.com/Fastest_Hash/ See http://www.sanmayce.com/Fastest_Hash/ and
https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function#FNV-1a_hash
NOTE: A lot of cast. Not really type nor alignement safe. NOTE: A lot of cast. Not really type nor alignement safe.
NOTE: Can be reduced to very few instructions if constant size argument. NOTE: Can be reduced to very few instructions if constant size argument.
*/ */
static inline uint32_t static inline uint32_t
m_core_hash (const void *str, size_t wrdlen) m_core_hash (const void *str, size_t length)
{ {
const uint32_t prime = 709607U; const uint32_t prime = 709607U;
uint32_t hash32 = 2166136261U ^ M_HASH_SEED; uint32_t hash32 = 2166136261U ^ M_HASH_SEED;
const uint8_t *p = (const uint8_t *)str; const uint8_t *p = (const uint8_t *)str;
assert (str != NULL);
assert ( ( (uintptr_t)p & (sizeof(uint32_t)-1) ) == 0); assert ( ( (uintptr_t)p & (sizeof(uint32_t)-1) ) == 0);
while (wrdlen >= 2*sizeof(uint32_t)) { assert ( length > 0);
const uint32_t *pui = (const uint32_t *) (uintptr_t) p;
hash32 = (hash32 ^ (m_core_rotl32a(pui[0],5) ^ pui[1])) * prime; while (length >= 2*sizeof(uint32_t)) {
wrdlen -= 2*sizeof(uint32_t); const uint32_t *ptr = (const uint32_t *) (uintptr_t) p;
hash32 = (hash32 ^ (m_core_rotl32a(ptr[0],5) ^ ptr[1])) * prime;
length -= 2*sizeof(uint32_t);
p += 2*sizeof(uint32_t); p += 2*sizeof(uint32_t);
} }
// Cases: 0,1,2,3,4,5,6,7 // Cases: 0,1,2,3,4,5,6,7
if (wrdlen & sizeof(uint32_t)) { if (length & sizeof(uint32_t)) {
const uint16_t *pui = (const uint16_t *) (uintptr_t) p; const uint32_t *ptr = (const uint32_t *) (uintptr_t) p;
hash32 = (hash32 ^ pui[0]) * prime; hash32 = (hash32 ^ ptr[0]) * prime;
hash32 = (hash32 ^ pui[1]) * prime; p += sizeof(uint32_t);
p += 2* sizeof(uint16_t);
} }
if (wrdlen & sizeof(uint16_t)) { if (length & sizeof(uint16_t)) {
const uint16_t *pui = (const uint16_t *) (uintptr_t) p; const uint16_t *ptr = (const uint16_t *) (uintptr_t) p;
hash32 = (hash32 ^ pui[0]) * prime; hash32 = (hash32 ^ ptr[0]) * prime;
p += sizeof(uint16_t); p += sizeof(uint16_t);
} }
if (wrdlen & 1) if (length & 1)
hash32 = (hash32 ^ *p) * prime; hash32 = (hash32 ^ *p) * prime;
return hash32 ^ (hash32 >> 16); return hash32 ^ (hash32 >> 16);
} }
@@ -690,8 +694,8 @@ m_core_hash (const void *str, size_t wrdlen)
if the type is recognized. if the type is recognized.
NOTE: Default case is not safe if the type is defined with the '[1]' trick. */ NOTE: Default case is not safe if the type is defined with the '[1]' trick. */
#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L #if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
#define M_HASH_INT32(a) ( (a) ^ ((a) << 11) ) #define M_HASH_INT32(a) ( (a) ^ ((a) << 11) ^ M_HASH_SEED )
#define M_HASH_INT64(a) ( ( (a) >> 33 ) ^ (a) ^ ((a) << 11) ) #define M_HASH_INT64(a) ( ( (a) >> 33 ) ^ (a) ^ ((a) << 11) ^ M_HASH_SEED )
#define M_HASH_DEFAULT(a) \ #define M_HASH_DEFAULT(a) \
_Generic((a)+0, \ _Generic((a)+0, \
int32_t: M_HASH_INT32(M_AS_TYPE(int32_t, a)), \ int32_t: M_HASH_INT32(M_AS_TYPE(int32_t, a)), \